This invention relates to apparatus and method for sampling liquid and solids-bearing liquid media such as sewage, particularly in explosive-atmosphere environments, by means of automatically functioning, pneumatically-operated apparatus.
In many flow streams it is desirable to monitor the contents of the flow by periodic sampling, as in the case of stream pollution control, sewage monitoring and industrial waste situations. Such monitoring is required by government in some cases. A variety of stream sampling devices have been proposed for these purposes. See, for example, U.S. Pat. Nos. 3,120,128; 3,438,262; 3,589,197; 3,750,477; and 3,795,347, and also British Pat. No. 720,161.
Increasing recognition of the explosive atmosphere hazard in sewage lines and other wastewater works has created a need for an explosion-proof sampling device. Electrically-operated devices must be either explosion proof or intrinsically safe (e.g., through use of extremely low voltage), to be operated in explosive atmospheres, or the device and/or the surrounding atmosphere must be purged with air. None of these methods provides absolute safety, and electrically-operated devices have proved dangerous. Several all-pneumatic samplers have previously been developed, but these devices have been underpowered, delicate, and undependable in sewage applications.
Of the above-cited patents, none shows a completely pneumatic sampler which avoids any reliance on electric circuitry, except U.S. Pat. No. 3,750,477, but the sampling apparatus disclosed in that patent is different from and without many advantages of the present invention. U.S. Pat. No. 3,795,347 does show a height-adjustable volume control tube as is included in the present invention described below, but the present sampler is all pneumatic and includes many other advantageous features not found in any of the apparatus of the cited patents.